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SubjectRe: [PATCH v2 1/6] SP800-90A Deterministic Random Bit Generator
Date
Am Montag, 17. März 2014, 08:34:06 schrieb Stephan Mueller:

> +static int drbg_seed(struct drbg_state *drbg, struct drbg_string *pers,
> + bool reseed)
> +{
> + int ret = 0;
> + unsigned char *entropy = NULL;
> + size_t entropylen = 0;
> + struct drbg_string data1;
> + struct drbg_string *data2;
> +
> + /* 9.1 / 9.2 / 9.3.1 step 3 */
> + if (pers && pers->len > (drbg_max_addtl(drbg)))
> + return -EINVAL;
> +
> + if (drbg->test_data) {
> + data1.buf = drbg->test_data->testentropy->buf;
> + data1.len = drbg->test_data->testentropy->len;
> + data1.next = NULL;
> + } else {
> + /* Gather entropy equal to the security strength of the DRBG.
> + * With a derivation function, a nonce is required in addition
> + * to the entropy. A nonce must be at least 1/2 of the
security
> + * strength of the DRBG in size. Thus, entropy * nonce is 3/2
> + * of the strength. The consideration of a nonce is only
> + * applicable during initial seeding. */
> + entropylen = (drbg_sec_strength(drbg->core->flags) / 8);

drbg_sec_strength returns the strength in bytes, thus the division by 8 must
be removed

> + if (!entropylen)
> + return -EFAULT;
> + if (!reseed)
> + /* make sure we round up strength/2 in
> + * case it is not divisible by 2 */
> + entropylen = ((entropylen + 1) / 2) * 3;
> +
> + entropy = kzalloc(entropylen, GFP_KERNEL);
> + if (!entropy)
> + return -ENOMEM;
> + get_random_bytes(entropy, entropylen);
> + drbg_string_fill(&data1, entropy, entropylen);
> + }
> +
> + /* concatenation of entropy with personalization str / addtl input) */
> + if (pers && 0 < pers->len) {
> + data2 = pers;
> + data2->next = NULL;
> + data1.next = data2;
> + }
> +
> + ret = drbg->d_ops->update(drbg, &data1, reseed);
> + if (ret)
> + goto out;
> +
> + drbg->seeded = true;
> + /* 10.1.1.2 / 10.1.1.3 step 5 */
> + drbg->reseed_ctr = 1;
> +
> +out:
> + if (entropy)
> + kzfree(entropy);
> + return ret;
> +}
> +

[...]
> +static unsigned int drbg_generate(struct drbg_state *drbg,
> + unsigned char *buf, unsigned int buflen,
> + struct drbg_string *addtl)
> +{
> + unsigned int len = 0;
> + struct drbg_state *shadow = NULL;
> +
> + if (0 == buflen || !buf)
> + return 0;
> + if (addtl && NULL == addtl->buf && 0 < addtl->len)
> + return 0;
> +
> + if (drbg_make_shadow(drbg, &shadow))
> + return 0;
> + /* 9.3.1 step 2 */
> + if (buflen > (drbg_max_request_bytes(shadow)))
> + goto err;
> + /* 9.3.1 step 3 is implicit with the chosen DRBG */
> + /* 9.3.1 step 4 */
> + if (addtl && addtl->len > (drbg_max_addtl(shadow)))
> + goto err;
> + /* 9.3.1 step 5 is implicit with the chosen DRBG */
> + /* 9.3.1 step 6 and 9 supplemented by 9.3.2 step c -- the spec is a
> + * bit convoluted here, we make it simpler */
> + if ((drbg_max_requests(shadow)) < shadow->reseed_ctr)
> + shadow->seeded = false;
> +
> + /* allocate cipher handle */
> + if (shadow->d_ops->crypto_init && shadow->d_ops->crypto_init(shadow))
> + goto err;
> +
> + if (shadow->pr || !shadow->seeded) {
> + /* 9.3.1 steps 7.1 through 7.3 */
> + if (drbg_seed(shadow, addtl, true))
> + goto err;
> + /* 9.3.1 step 7.4 */
> + addtl = NULL;
> + }
> + /* 9.3.1 step 8 and 10 */
> + len = drbg->d_ops->generate(shadow, buf, buflen, addtl);

This needs to be shadow->d_ops
> +
> + /* 10.1.1.4 step 6, 10.1.2.5 step 7, 10.2.1.5.2 step 7 */
> + shadow->reseed_ctr++;
> +
> +err:
> + if (shadow->d_ops->crypto_fini)
> + shadow->d_ops->crypto_fini(shadow);
> + drbg_restore_shadow(drbg, &shadow);
> + return len;
> +}

Ciao
Stephan
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